As the human eye ages, its ability to change its power to image objects at different distances wanes. This decline is called “presbyopia” and it affects all humans. A similar inability to adjust optical power of the eye's lens occurs in patients who have their natural lens replaced by an artificial lens (e.g. after cataract surgery). Thus the challenges of seeing at multiple distances faced by presbyopes are shared by pseudophakes. Currently, there is no cure for presbyopia, and there is no perfect optical treatment that will restore this full range of vision those skilled in the art and practice call “accommodation”. Surrogate optical devices and strategies have been developed that are designed to increase the range of distances that can be seen (depth of field). Such devices produce what is known as “pseudo-accommodation”. That is, they increase the depth of field without changing power of the eye itself. All of these devices and strategies are inferior to normal accommodation, and all require compromises by the presbyopic patient. There is an obvious need to develop improved devices and strategies to enhance the vision quality of presbyopes.
There are several well-established strategies for increasing the depth of field of presbyopes. The most simple involves implementing some form of small (“pinhole”) pupil, which increases the depth of field without changing the optical characteristics of the underlying optics. Such a strategy fails in low light levels and can severely limit the size of the visual field. More typical are strategies that actively implement some optical lens or device that focuses light on the retina from targets located at different distances. One such strategy employs standard monofocal lenses of different powers in the two eyes, called “monovision”. Most strategies, however, employ lenses that contain more than one power, either bifocal, trifocal, or multifocal lenses.
When implemented as a spectacle lens, the different powers present in bifocals, trifocal or multifocals are distributed across the spectacle lens, and by a combination of head and eye movements, the patient can select the region of the spectacle lens that provides a focused image on the retina (and thus high quality vision) for targets are different distances. This approach, of selecting different powers by eye and head movements will not work for soft contact lenses (CLs) or intra-ocular lenses (IOLs) or correction created in or on the cornea via refractive surgery because the lenses or corneal corrections move with the eye. Therefore, irrespective of gaze direction, the patient is always looking through the same optics.
Bifocal, Trifocal and multifocal optical corrections for presbyopes that move with the eye (corrections in or on the cornea (corneal inlays or onlays, other refractive surgeries), CLs and IOLs) must therefore contain multiple optical powers within the same or adjacent regions of the optical device or strategy that both contribute to the retinal image. That is, unlike the presbyopic spectacle lens correction in which the patient sequentially selects the physical lens location of the most appropriate optical power, patients with presbyopic corrections in CL, IOL, or refractive surgery simultaneously employ different optical powers, and thus these devices and strategies are referred to as “simultaneous vision” lenses or corrections.
Herein lies the core problem faced by CL, IOL, and refractive surgery corrections that aim to provide increased depth of field for presbyopic patients. In addition to the light that is well focused on the retina by one of the optical powers, there is simultaneously present out of focus light that is being imaged by the other power(s) in the simultaneous vision correction. The quality of the retinal image (and therefore vision of the patient) is, therefore, determined by this combination of focused and defocused light. Most of the ophthalmic industry's efforts to provide improved optical corrections for the presbyope have centered on manipulating and enhancing the focused portion of this light. The invention described in this patent is designed to improve vision of presbyopes by reducing the impact of the defocused portion of the light.
The core optical characteristic of all simultaneous vision corrections for presbyopia is the increased depth of field provided. The primary determinant of the increased depth of field is the range of optical powers within the optical device or refractive surgery. Numerous presbyopic corrections for presbyopes have been marketed and still others invented that distribute power within the lens (or refractive surgery) using a wide range of strategies. Very simply, such optical corrections can be designed to have 2 powers (bifocals), three powers (trifocals), or multiple powers (multifocals). One strategy for creating a multifocal lens is to gradually change the power of the lens from the center toward the edge. This can be achieved by introducing large amounts of spherical aberration (SA) into the lens, which can either make the lens periphery less powerful than the lens center (negative SA, see U.S. Pat. No. 7,261,412 B2, Aug. 28, 2007 and U.S. Pat. No. 0,051,876 A1, 2009). This lens would have maximum power at its center, and thus would be referred to as a “center-near” design in that increased power is required to focus near targets. Alternately, a similar strategy generates a “center-distance” design by adding positive SA to the lens (see U.S. Pat. No. 5,089,024, Feb. 18, 1992). With both of these strategies, SA is manipulated in the lens design to increase the range of powers present and thus increase the depth of field.
There is a different general strategy that employs discrete optical powers, e.g. a bifocal with two powers, or a tri-focal with three powers, rather than a gradual change in power across the lens. In such designs, the optical quality of the retinal image produced when one of the optics is in focus can be enhanced by including within each zone a complete (e.g. U.S. Pat. No. 5,220,359, Jun. 15, 1993, and World Patent # WO 2005/019906 A1) or partial (e.g. U.S. Pat. No. 7,118,214, Oct. 10, 2006) correction for the spherical aberration (SA) present within the human eye. Because the human eye typically has positive SA, these lenses correct this by introducing negative SA. However, there may be some eyes with negative SA, so these lenses would introduce positive SA to correct it. In many such inventions, SA is first measured using some form of aberrometer.
When a controlled level of SA is introduced into a lens, this lens is often described as being “aspheric”. In a third general design strategy for simultaneous vision presbyopic corrections, SA and/or other radially symmetric asphericities are employed to control the transition between zones of different powers. That is, instead of have a spatially discrete transition, the power is gradually changed across a transition region of the lens. This gradual change in power is sometimes referred to as an asphericity, or SA. Several inventions employ such asphericities (e.g. U.S. Pat. No. 6,457,826 B1, World Patent WO 2007/015001 A1, World Patent # WO 0221194 A2).
Two other strategies have been implemented that employ SA or other radially symmetric asphericities as part of a presbyopic or pseudophakic correction. First, contrary to the designs that employ a SA correction within the different optical zones to improve focused mage quality, one can introduce SA within the different zones with the goal of increasing the depth of field (e.g. U.S. Pat. No. 0,176,572 A1, 2006). Also, increased depth of field can be introduced into what is designed to be a monofocal correction by adding small asphericities to the optic (U.S. Pat. No. 0,230,299 A1, 2004).
All of the above designs that employ SA or similar asphericities are designed to either improve the quality of the focused image within a simultaneous vision correction OR to increase the depth of field in the same type of correction. One invention sought to employ SA control in a simultaneous vision lens to reduce the visibility of the defocused image (patent application WO 2010/014767). This strategy was simple: introduce specific SA into the bifocal correction that would correct for the eye's SA, and thus maximize the quality of the focused portion of the light. When the focused portion of the light was indeed well focused, this invention claimed (with no supporting evidence) that the visibility of the defocused image (often referred to as a “ghost” image) would be reduced. Of course, numerous previous patents had been awarded that already employed SA correction within the bifocal (see above). We have invented a novel strategy for employing controlled SA (or similar asphericity) to minimize the visibility of the out of focus “ghost” image generated by bifocal, trifocal or multifocal presbyopic correction (see detailed description below).